Large effective area optical fiber

ABSTRACT

An optical waveguide fiber having a relatively large effective area which exhibits low attenuation, low PMD and low microbending sensitivity. A step-index refractive index profile is advantageously used.

RELATED APPLICATIONS

This application claims the benefit of the priority date of commonlyassigned U.S. Provisional Patent Application Nos. 60/254,909 filed Dec.12, 2000 and 60/276,350 filed Mar. 16, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

A single mode optical waveguide fiber for use in telecommunicationsystems and more particularly, a waveguide fiber which reducesnon-linear dispersion effects, combines bend resistance, lowpolarization mode dispersion (PMD), low attenuation, and large effectivearea features desired, for example, in underground and underseaapplications is disclosed herein.

2. Technical Background

Optical amplifier technology and wavelength division multiplexingtechniques are typically required in telecommunication systems thatrequire high power transmissions for long distances. Undesirablenon-linear effects become more pronounced for higher powers and/orlonger distances. The definition of high power and long distances ismost meaningful in the context of a particular telecommunication systemwherein a bit rate, a bit error rate, a multiplexing scheme, and perhapsoptical amplifiers are specified. Additional actors, known to thoseskilled in the art, have impacted upon the definition of high power andlong distance. However, for most purposes, high power could beconsidered to be an optical power greater than about 10 mW. In someapplications, single power levels of 1 mW or less are still sensitive tonon-linear effects, so that the effective area is still an importantconsideration in such lower power systems. A long distance could beconsidered to be an application in which the distance between opticalregenerators or repeaters or amplifiers is in excess of 50 km or more.Regenerators are to be distinguished from repeaters that make use ofoptical amplifiers. Repeater spacing, especially in high data densitysystems, can be less than half the regenerator spacing. To provide asuitable waveguide for a multiplex transmission, the total dispersionshould be low, but not zero, and have a low dispersion slope over thewindow of operating wavelength.

Generally, an optical waveguide fiber having a large effective area(A_(eff)) reduces non-linear optical effects, including self-phasemodulation, four-wave-mixing, cross-phase modulation, and non-linearscattering processes, all of which can cause degradation of signals inhigh powered systems. In general, a waveguide fiber having a segmentedcore can provide a large effective area while limiting the non-linearoptical effects.

The mathematical description of these non-linear effects includes theratio, P/A_(eff), where P is the optical power. For example, anon-linear optical effect can be described by an equation containing theterm, exp [P×L_(eff)/A_(eff)], where L_(eff) is effective length. Thus,an increase in A_(eff) produces a decrease in the non-linearcontribution to the degradation of a light signal. On the other hand, anincrease in effective area of an optical waveguide fiber typicallyresults in an increase in microbending induced losses which attenuatesignal transmission through a fiber. The microbending losses becomeincreasingly significant over long distances or spacing betweenregenerators, amplifiers, transmitters and/or receivers.

Optical amplifier technology and/or wavelength division multiplexingtechniques are typically employed in communication systems which requireone gigabyte per second and higher transmission rates. Thus waveguidefiber manufacturers have designed waveguides that are less susceptibleto non-linear effects induced by higher power signals or by four wavemixing in multiplexing systems. Preferred waveguide fibers have lowlinear dispersion and low attenuation as well. Furthermore, fiberpolarization mode dispersion (PMD) may be a major contributor to overallsystem PMD. Therefore, a suitable waveguide fiber should also have lowPMD. Lower fiber PMD can also provide upgrade paths for high bit ratetransmission (e.g. 40 Gbs and higher) in existing or upgraded systems.In addition, the waveguide fiber preferably displays these propertiesover a particular extended wavelength range in order to accommodatewavelength division multiplexing used for multiple channel transmission.

SUMMARY OF THE INVENTION

One aspect of the optical waveguide fiber disclosed herein relates to arelatively large effective area single mode optical waveguide fiber thatoffers low microbending sensitivity. The fibers disclosed hereinpreferably include a single segment core. The core region is describedby a refractive index profile, a relative refractive index percent, andan outer radius. The optical waveguide fiber further includes a cladlayer surrounding and in contact with the core. Unless indicatedotherwise, the effective area described herein corresponds to awavelength of about 1550 nmn.

Preferably, the effective area of the fibers disclosed herein is greaterthan or equal to about 90 μm², and exhibits microbending of less than orequal to about 3.0 dB/m, more preferably less than or equal to about 2.0dB/m, even more preferably less than or equal to about 1.5 dB/m, evenstill more preferably less than or equal to about 1.0 dB/m, yet stillmore preferably less than or equal to about 0.8 dB/m, and even stillmore preferably less than or equal to about 0.5 dB/m.

The core region and cladding layer preferably define a step-indexrefractive index profile. Preferably, the fibers disclosed herein has amaximum relative index Δ₁% of between about 0.20% and about 0.35%, morepreferably between about 0.24% and about0.33%, even more preferablybetween about 0.26% and about0.32%, and still more preferably betweenabout 0.27% and about0.31%. Preferably, the core radius of the fibersdisclosed herein, measured at half the maximum or peak relative index,is between about 4.0 μm and about 7.0 μm, more preferably between about4.5 μm and about 6.5 μm, and still more preferably is between about 5.0μm and about 6.2 μm.

The fibers disclosed herein further preferably comprise a primarycoating surrounding the cladding and a secondary coating, also known asan outer primary coating, surrounding the primary coating. The primarycoating is preferably selected to have a modulus of elasticity of lessthan about 5 MPa, more preferably less than about 3 MPa, and even morepreferably less than about 1.5 MPa. Preferably, the modulus ofelasticity of the secondary coating is greater than 700 Mpa, morepreferably greater than 800 Mpa, and even more preferably over 900 MPa.

Preferably, the fibers disclosed herein comprise a core region of silicawhich is up-doped with germania, and a cladding of silica. Preferably,the cladding contains no down-dopants. Even more preferably, thecladding contains no fluorine. Most preferably, the cladding comprisespure or substantially pure silica.

In another aspect, the optical waveguide fiber disclosed herein relatesto a relatively large effective area single mode optical waveguide fiberhaving a step-index profile. Preferably, the effective area of thefibers disclosed herein is greater than or equal to about 90 μm². In oneor more preferred embodiments, the effective area is between about 90μm² and about 115 μm², more preferably between about 95 μm² and about110 μm².

Preferably, the fibers disclosed herein have a maximum relative indexΔ₁% of between about 0.20% and about 0.35%, more preferably betweenabout 0.24% and about 0.33%, still more preferably between about 0.26%and about 0.32%, and yet more preferably between about 0.27% and about0.31%. Preferably, the core radius of the fibers disclosed herein,measured at half the maximum or peak relative index, is between about4.0 μm and about 7.0 μm, more preferably between about 4.5 μm and about6.5 μm, even more preferably between about 5.0 μm and about 6.2 μm.

Preferably, the fibers disclosed herein comprise a core region of silicawhich is up-doped with germania, and a cladding of silica. Preferably,the cladding contains no down-dopants. Even more preferably, thecladding contains no fluorine. Most preferably, the cladding comprisespure, or substantially pure, silica.

The fibers disclosed herein preferably exhibit an attenuation at awavelength of about 1550 nm of less than or equal to about 0.25 dB/km,more preferably less than or equal to about 0.22 dB/km, even morepreferably less than or equal to about 0.2 dB/km, yet more preferablyless than or equal to about 0.19 dB/kyn, and most preferably less thanabout 0.185 dB/km.

In preferred embodiments, the fibers disclosed herein exhibit a totaldispersion at a wavelength of about 1560 nm of preferably within therange of about 16 ps/nm-km to about 22 ps/nm-km, more preferably withinthe range of about 17 ps/nm-km to about 21 ps/nm-km, and even morepreferably within the range of about 18 ps/nm-km to about 20 ps/nm-km.

The total dispersion slope at a wavelength of about 1550 nm of thefibers disclosed herein is preferably less than or equal to about 0.09ps/nm²-km. In one or more preferred embodiments, the total dispersionslope at a wavelength of about 1550 nm of the fibers disclosed herein ispreferably between about 0.045 ps/nm²-km and about 0.075 ps/nm²-km, evenmore preferably between about 0.05 ps/nm²-km and about 0.07 ps/nm²-km,still more preferably between about 0.055 ps/nm²-km and about 0.065ps/nm²-km.

In yet another aspect, the optical waveguide fiber disclosed hereinrelates to a relatively large effective area single mode opticalwaveguide fiber having a maximum relative index Δ₁% of between about0.20% and about 0.35%, more preferably between about 0.24% and about0.33%, even more preferably between about 0.26% and about 0.32%, andstill more preferably between about 0.27% and about 0.31%. Preferably,the core radius of the fibers disclosed herein, measured at half themaximum or peak relative index, is between about 4.0 μm and about 7.0μm, more preferably between about 4.5 μm and about 6.5 μm, and stillmore preferably between about 5.0 μm and about 6.2 μm.

Preferably, the refractive index profile of the fibers disclosed hereinis of the step-index type. Preferably, the fibers disclosed hereincomprise a core region of silica which is up-doped with germania, and acladding of silica. Preferably, the cladding contains no down-dopants.Even more preferably, the cladding contains no fluorine. Mostpreferably, the cladding comprises pure, or substantially pure, silica.

In still another aspect, the optical waveguide fiber disclosed hereinrelates to a relatively large effective area single mode opticalwaveguide fiber which comprises an up-doped core region or whichcomprises a germano-silicate core region or which comprises agermania-doped silica core. Preferably, the fibers disclosed hereincomprise a core region of silica which is up-doped with germaniasurrounded by a cladding of silica. Preferably, the cladding contains nodown-dopants. Even more preferably, the cladding contains no fluorine.Most preferably, the cladding comprises pure, or substantially pure,silica. Preferably, the effective area is greater than or equal to about90 μm².

In yet another aspect, the optical waveguide fiber disclosed hereinrelates to a relatively large effective area single mode opticalwaveguide fiber which exhibits low PMD. Preferably, the effective areais greater than or equal to about 90 μm². Preferably, the PMD exhibitedby the fibers disclosed herein is less than about 0.1 ps/km^(1/2)(unspun), more preferably less than about 0.08 ps/km^(1/2) (unspun),even more preferably less than about 0.05 ps/km^(1/2) (unspun), stillmore preferably less than about 0.03 ps/km^(1/2) (unspun), even stillmore preferably less than about 0.02 ps/kr^(1/2) (unspun). In onepreferred embodiment, the optical waveguide fiber disclosed hereinrelates to a single mode optical waveguide fiber having an effectivearea greater than or equal to about 90 μm² and which a PMD of less thanabout 0.05 ps/km^(1/2) (unspun). In another preferred embodiment, theoptical waveguide fiber disclosed herein relates to a single modeoptical waveguide fiber having an effective area greater than or equalto about 90 μm² and which a PMD of less than about 0.02 ps/km^(1/2)(unspun).

Preferably, the fibers disclosed herein have a step-index profile, andfurther preferably comprises a core region of silica, which is up-dopedwith germania, the core region being surrounded by a cladding of silica.Preferably, the cladding contains no down-dopants. Even more preferably,the cladding contains no fluorine. Most preferably, the claddingcomprises pure, or substantially pure, silica.

In another aspect, the optical waveguide fiber disclosed herein relatesto an optical waveguide fiber comprising a core having a refractiveindex profile defined by a radius and a relative refractive indexpercent, wherein the core contains germania, and a clad layersurrounding and in contact with the core and having a refractive indexprofile defined by a radius and a relative refractive index percent,wherein the core and the clad layer provide an effective area greaterthan about 90 μm², and wherein the fiber contains substantially nofluorine. Preferably, the core and the clad layer provide an effectivearea of between about 90 μm² and about 115 μm², and more preferably thecore and the clad layer provide an effective area of between about 95μm² and about 110 μm². In a preferred embodiment, the core and the cladlayer provide an effective area of about 101 μm². Preferably, the coreand the cladding define a step-index profile. Preferably, the relativerefractive index of the core is within the range of from about 0.20% toabout 0.35%, more preferably the relative refractive index of the coreis within the range of from about 0.24% to about 0.33%. Preferably, theradius of the core is within the range of from about 4.0 μm to about 7.0μm, more preferably the radius of the core is within the range of fromabout 4.5 μm to about 6.5 μm. Preferably, the core has an alpha greaterthan about 5, and more preferably the core has an alpha between about 7and about 14. Preferably, the fiber has a cabled cutoff wavelength ofless than or equal to about 1500 nm, more preferably the fiber has acabled cutoff wavelength of between about 1200 nm and about 1500 nm. Ina preferred embodiment, the fiber has a cabled cutoff wavelength ofbetween about 1250 nm and about 1400 nm. In another preferredembodiment, the fiber has a cabled cutoff wavelength of between about1300 nm and about 1375 nm. Preferably, the fiber exhibits macrobendingloss less than about 15 dB/m in a 20 mm, 5 turn test, more preferablyless than about 10 dB/m in a 20 mm, 5 turn test, and even morepreferably less than about 5 dB/m in a 20 mm, 5 turn test. The fiberpreferably further comprises a primary coating surrounding the cladlayer and a secondary coating surrounding the primary coating. Theprimary coating preferably has a modulus of elasticity of less thanabout 5 MPa. The secondary coating preferably has a modulus ofelasticity of greater than about 700 MPa. Preferably, the fiber exhibitsmicrobending loss of less than about 3.0 dB/m, more preferably less thanabout 2.0 dB/m, even more preferably less than about 1.5 dB/m, stillmore preferably less than about 1.0 dB/m, even still more preferablyless than about 0.8 dB/m, and still more preferably less than about 0.5dB/m. Preferably, the attenuation of the optical fiber at 1383 nm is notmore than 0.1 dB/km higher than its attenuation at 1310 nm. Morepreferably, the attenuation of the optical fiber at 1383 nm is not morethan 0.05 dB/km higher than its attenuation at 1310 nm. Still morepreferably, the attenuation of the optical fiber at 1383 nm is not morethan 0.01 dB/km higher than its attenuation at 1310 nm. Even still morepreferably, the attenuation of the optical fiber at 1383 nm is less thanor about equal to than its attenuation at 1310 nm. Preferably, the fiberexhibits a PMD of less than about 0.1 ps/km^(1/2), more preferably lessthan about 0.05 ps/km^(1/2), even more preferably less than about 0.01ps/km^(1/2), and still more preferably less than or equal to about 0.006ps/km^(1/2). Preferably, the fiber exhibits an attenuation at awavelength of about 1550 nm of less than or equal to about 0.25 dB/km,more preferably less than or equal to about 0.22 dB/km, even morepreferably less than or equal to about 0.2 dB/km, and still morepreferably less than about 0.185 dB/km. Preferably, the fiber exhibits atotal dispersion within the range of about 16 ps/nm-km to about 22ps/nm-km at a wavelength of about 1560 nm.

In another aspect, the optical waveguide fiber disclosed herein relatesto an optical waveguide fiber comprising a core having a refractiveindex profile defined by a radius and a relative refractive indexpercent with an alpha greater than about 5, wherein the core containsgermania and wherein the relative refractive index of the core is withinthe range of about 0.20% to about 0.35% and the radius of the core iswithin the range of from about 4.0 μm to about 7.0 μm, and a clad layersurrounding and in contact with the core and having a refractive indexprofile defined by a radius and a relative refractive index percent,wherein the fiber contains substantially no fluorine. Preferably, therelative refractive index of the core is within the range of from about0.24% to about 0.33%. Preferably, the radius of the core is within therange of from about 4.5 μm to about 6.5 μm. Preferably, the core has analpha between about 7 and about 14. Preferably, the core and thecladding define a step-index profile. Preferably, the fiber furthercomprises a primary coating surrounding the clad layer, and a secondarycoating surrounding the primary coating. The primary coating preferablyhas a modulus of elasticity of less than about 5 MPa. The secondarycoating preferably has a modulus of elasticity of greater than about 700MPa. Preferably, the attenuation of the optical fiber at 1383 nm is notmore than 0.1 dB/km higher than its attenuation at 1310 nm. Morepreferably, the attenuation of the optical fiber at 1383 nm is not morethan 0.05 dB/km higher than its attenuation at 1310 nm. Even morepreferably, the attenuation of the optical fiber at 1383 nm is not morethan 0.01 dB/km higher than its attenuation at 1310 nm. Still morepreferably, the attenuation of the optical fiber at 1383 nm is less thanor about equal to than its attenuation at 1310 nm. Preferably, the fiberexhibits a PMD of less than about 0.1 ps/km^(1/2), more preferably lessthan about 0.05 ps/km^(1/2), even more preferably less than about 0.01ps/km^(1/2), still more preferably even more preferably less than about0.006 ps/km^(1/2).

In another aspect, the optical waveguide fiber disclosed herein relatesto an optical waveguide fiber comprising a core having a refractiveindex profile defined by a radius and a relative refractive indexpercent, wherein the core contains germania, and a clad layersurrounding and in contact with the core and having a refractive indexprofile defined by a radius and a relative refractive index percent,wherein the core and the clad layer provide an effective area greaterthan about 90 μm{fraction (1/2)}, and wherein the fiber exhibits a PMDof less than about 0.1 ps/km^(1/2).

In another aspect, the optical waveguide fiber disclosed herein relatesto an optical waveguide fiber comprising a core having a refractiveindex profile defined by a radius and a relative refractive indexpercent, wherein the core contains germania and a clad layer surroundingand in contact with the core and having a refractive index profiledefined by a radius and a relative refractive index percent, wherein thecore and the clad layer provide an effective area greater than about 90μm{fraction (1/2)}, and wherein the attenuation of the optical fiber at1383 nm is not more than 0.1 dB/km higher than its attenuation at 1310nm.

In another aspect, an optical signal transmission system disclosedherein comprises a transmitter, a receiver, and an optical transmissionline optically coupled to the transmitter and receiver, wherein theoptical transmission line comprises at least one optical fiber sectionhaving a core and a clad layer which define a step-index profile thatprovides an effective area greater than about 90 μm², wherein the fiberexhibits an attenuation at 1383 nm which is not more than 0.1 dB/kmhigher than its attenuation at 1310 nm. The the core preferably containsgermania. The fiber section preferably contains substantially nofluorine. Preferably, the fiber section exhibits a total dispersionwithin the range of about 16 ps/nm-km to about 22 ps/nm-km at awavelength of about 1560 nm. Preferably, the fiber section exhibits aPMD of less than about 0.1 ps/km^(1/2). In a preferred embodiment, atleast one Raman amplifier is optically coupled to the optical fibersection. Preferably, the system further comprises a multiplexer forinterconnecting a plurality of channels capable of carrying opticalsignals onto the optical transmission line, wherein at least one of theoptical signals propagates at a wavelength between about 1300 nm and1625 nm. In a preferred embodiment, at least one of the optical signalspropagates at a wavelength between about 1330 nm and 1480 nm.Preferably, the system is capable of operating in a coarse wavelengthdivision multiplex mode.

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a preferred embodiment ofan optical waveguide fiber in accordance with the present invention;

FIG. 2 is a diagram of a waveguide fiber refractive index profile of asingle segment core optical waveguide according to the presentinvention;

FIG. 3 is a schematic view of a fiber optic communication systememploying an optical fiber of the present invention;

FIG. 4 is a schematic representation of laydown of a soot preform;

FIG. 5 is a schematic representation of a preform having both ends ofits centerline hole plugged;

FIG. 6 is a closeup view of the plugged preform of FIG. 7 showing thetop plug;

FIG. 7 is a schematic representation of a preform or an optical fiberhaving a closed centerline region;

FIG. 8 shows a refractive index profile measurement corresponding to apreferred embodiment of an optical waveguide fiber in accordance withthe present invention;

FIG. 9 is a graph of measured loss or attenuation for the preferredembodiment of the optical fiber having a refractive index profilecorresponding to FIG. 8; and

FIG. 10 is a refractive index profile corresponding to another preferredembodiment of an optical waveguide fiber in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Additional features and advantages of the invention will be set forth inthe detailed description which follows and will be apparent to thoseskilled in the art from the description or recognized by practicing theinvention as described in the following description together with theclaims and appended drawings.

Definitions

The following terminology and definitions are commonly used in the art.

The radii of the segments of the core are defined in terms of the indexof refraction of the material of which the segment is made. A particularsegment has a first and a last refractive index point. A central segmenthas an inner radius of zero because the first point of the segment is onthe center line. In the case of step index, single segment index ofrefraction profiles, which are preferred herein, the index of refractiontypically reaches a peak value and then falls as the radius increases.The outer radius of such central segment is the radius drawn from thewaveguide center line to the one-half peak point of the refractive indexof the central segment. For a segment having a first point away from thecenter line, the radius from the waveguide center line to the locationof its first refractive index point is the inner radius of that segment.Likewise, the radius from the waveguide center line to the location ofthe one-half peak refractive index point of the segment is the outerradius of that segment. The segment radii may be conveniently defined ina number of ways. In this application, radii are defined in accord withthe figures, described in detail below.

The effective area is generally defined as,

A _(eff)=2π(r dr)²/(r dr)

wherein the integration limits are zero to ∞, and E is the electricfield associated with the propagated light.

The mode field diameter, D_(mf), is measured using the Peterman IImethod wherein, 2w=D_(mf) and w²=(2 r dr/dE/dr) ² r dr), the intergrallimits being 0 to ∞.

The relative index or relative refractive index of a segment, Δ%, asused herein, is defined by the equation,

 Δ%=100×(n _(i) ² −n _(c) ²)/2n _(c) ²

where n_(i) is the maximum refractive index of the index profile segmentdenoted as i, and n_(c), the reference refractive index, is taken to bethe minimum index of the clad layer. Every point in the segment has anassociated relative index.

The term refractive index profile or index profile is the relationbetween Δ% or refractive index and radius over a selected segment of thecore.

Total dispersion, usually referred to as dispersion, is defined as thealgebraic sum of waveguide dispersion and material dispersion. Totaldispersion for single-mode fibers is also referred to as chromaticdispersion in the art. The units of total dispersion are ps/nm-km.

The bend resistance of a waveguide fiber is expressed as inducedattenuation under prescribed test conditions. One bend test referencedherein is the macrobend test. Standard macrobend test conditions include100 turns of waveguide fiber around a 75 mm diameter mandrel and 1 turnof waveguide fiber around a 32 mm diameter mandrel. In each testcondition the bend induced attenuation, in units of dB/(unit length), ismeasured. In the present application, the macrobend test used is 5 turnsof the waveguide fiber around a 20 mm diameter mandrel, a more demandingtest which is required for the more severe operating environment of thepresent waveguide fiber.

Another bend test referenced herein is the lateral load microbend test.In this test a prescribed length of waveguide fiber is placed betweentwo flat plates. A #70 wire mesh is attached to one of the plates. Aknown length of waveguide fiber is sandwiched between the plates and areference attenuation is measured while the plates are pressed togetherwith a force of 30 newtons. A 70 newton force is then applied to theplates and the increase in attenuation in dB/m is measured. Thisincrease in attenuation is the lateral load attenuation of thewaveguide.

Waveguide designs which also are relatively easy to manufacture andwhich permit management of dispersion are favored, because of their lowcost and added flexibility. Manufacturing costs are a significant factorin determining which fiber profile designs are practical to manufactureon a large scale. Fiber profile designs that include multiple core andcladding segments, as well as those fiber profile designs that includesignificant up-doping and/or down-doping of those segments are typicallymore difficult and more expensive to manufacture. Cores made ofGeO₂—SiO₂ are less difficult and less expensive to manufacture thanother types of cores, particularly those that include fluorine in thecore, or pure silica in the central region of the core.

Preferably, the fibers disclosed herein are made by a vapor depositionprocess. Even more preferably, the fibers disclosed herein are made byan outside vapor deposition (OVD) process. Thus, for example, known OVDlaydown and draw techniques may be advantageously used to produce theoptical waveguide fiber disclosed herein. Other processes, such asmodified chemical vapor deposition (MCVD) may be used. Thus, therefractive indices and the cross sectional profile of the opticalwaveguide fibers disclosed herein can be accomplished usingmanufacturing techniques known to those skilled in the art including,but in no way limited to, OVD and MCVD processes.

The fibers disclosed herein provide relatively low cost large effectivearea fibers that exhibit low PMD, improved bend resistance, and/or lowattenuation, and which can effectively reduce non-linear dispersioneffects. The optical waveguide described and disclosed herein preferablyis of the step-index type, or in other words, the inventive opticalwaveguide fiber preferably has only a single segment core surrounded bya clad layer which preferably has a refractive index lower than that ofthe core.

FIG. 1 is a schematic representation (not to scale) of a preferredembodiment of an optical waveguide fiber disclosed herein having asingle core segment 12 and a cladding or clad layer 14. Preferably, thecladding 14 is pure or substantially pure silica. The cladding 14 issurrounded by a primary coating P and a secondary coating S.

FIG. 2 shows the relative refractive index percent (Δ%) charted versuswaveguide radius of a preferred embodiment of the optical waveguidefiber disclosed herein. The core 12, as referred to herein, can thus bedescribed by a refractive index profile, relative refractive indexpercent, Δ₁%, and an outside radius, r₁. As seen in FIG. 2, the cladlayer has a refractive index of n_(c) surrounding the core, wherein theoutside radius r₁ of the core can be measured at a half-maximum point.That is, the outer radius 18, r₁, of the core 12 illustrated is about5.15 μm as measured from the fiber centerline to the vertical linedepending from the half maximum relative index point of the descendingportion of core 12. The half maximum point is determined using the cladlayer, i.e., Δ%=0, as referenced, shown by dashed line 17. For example,in FIG. 2, the core 12 has a peak refractive index or maximum relativeindex Δ₁% of about 0.295%, thus, relative to the Δ%=0 of the clad layer,the magnitude is about 0.295%. Dashed vertical line 20 depends from the0.1475% point, which is half of the maximum magnitude of Δ₁%.

FIG. 2 illustrates a general representation of the core refractive indexprofile which shows relative refractive index percent (Δ%) chartedversus waveguide radius. Although FIG. 2 shows only a single segmentcore, it is understood that the functional requirements may be met byforming a core having more than a single segment. However, embodimentshaving fewer segments are usually easier to manufacture and aretherefore preferred.

The index profile structure characteristic of the novel waveguide fiberis shown by core segment 12 having a positive Δ%. Central segment 12 ofthe illustrated waveguide fiber core has a step-shaped or step-indexprofile. The refractive index profile may be adjusted to reach a coredesign which provides the required waveguide fiber properties.Preferably, the optical waveguide fiber disclosed herein is notdispersion shifted.

It should be noted that line 14 of FIG. 2 represents the refractiveindex of the cladding which is used to calculate the refractive indexpercentage of the segments. Diffusion of dopant during manufacturing ofwaveguide fiber may cause rounding of the corners of the profiles, asillustrated in FIG. 2, and may cause a center line refractive indexdepression as represented by dotted line 16. It is possible, but oftennot necessary, to compensate somewhat for such diffusion, for example,in the doping step.

The core region and cladding layer preferably define a step-indexrefractive index profile. Preferably, the fibers disclosed herein have amaximum relative index Δ₁% of between about 0.20% and about 0.35%, morepreferably between about 0.24% and about 0.33%, even more preferablybetween about 0.26% and about 0.32%, and still more preferably betweenabout 0.27% and about 0.31%. Preferably, the core radius of the fibersdisclosed herein, measured at half the maximum or peak relative index,is between about 4.0 μm and about 7.0 μm, more preferably between about4.5 μm and about 6.5 μm, and still more preferably between about 5.0 μmand about 6.2 μm.

Preferably, the effective area of the fibers disclosed herein is greaterthan or equal to about 90 μm². In one or more preferred embodiments, theeffective area is between about 90 μm² and about 115 μm², morepreferably between about 95 μm² and about 110 μm². One or more preferredembodiments of the optical waveguide fiber disclosed herein may have aneffective area of between about 96 μm² and about 105 μm², and morepreferably between about 99 μm² and about 102 μm².

The mode field diameter (MFD) of the fibers disclosed herein ispreferably greater than about 10 μm. In preferred embodiments, theoptical waveguide fiber disclosed herein may have an MFD of betweenabout 10.0 μm and about 13.0 μm, and more preferably between about 10.0μm and about 13.0 μm.

Preferably, the fibers disclosed herein exhibit microbending of lessthan or equal to about 3.0 dB/m, more preferably less than or equal toabout 2.0 dB/m, even more preferably less than or equal to about 1.5dB/m, even still more preferably less than or equal to about 1.0 dB/m,yet still more preferably less than or equal to about 0.8 dB/m, and evenstill more preferably less than or equal to about 0.5 dB/m. Even morepreferably, these values of microbending are achieved with an effectivearea of greater than about 90 μm².

The fibers disclosed herein preferably exhibit an attenuation at awavelength of about 1550 nm of less than or equal to about 0.25 dB/km,more preferably less than or equal to about 0.22 dB/km, even morepreferably less than or equal to about 0.2 dB/km, yet more preferablyless than or equal to about 0.19 dB/km, and most preferably less thanabout 0.185 dB/km.

In preferred embodiments, the fibers disclosed herein exhibit a totaldispersion at a wavelength of about 1560 nm of preferably within therange of about 16 ps/nm-km to about 22 ps/nm-km, more preferably withinthe range of about 17 ps/nm-km to about 21 ps/nm-km, and even morepreferably within the range of about 18 ps/nm-km to about 20 ps/nm-km.

The total dispersion slope at a wavelength of about 1550 nm of thefibers disclosed herein is preferably less than or equal to about 0.09ps/nm²-km. In one or more preferred embodiments, the total dispersionslope at a wavelength of about 1550 nm of the fibers disclosed herein ispreferably between about 0.045 ps/nm²-km and about 0.075 ps/nm²-km, evenmore preferably between about 0.05 ps/nm²-km and about 0.07 ps/nm²-km,still more preferably between about 0.055 ps/nm²-km and about 0.065ps/nm²-km.

Preferably, the PMD exhibited by the fibers disclosed herein is lessthan about 0.1 ps/km^(1/2) (unspun), more preferably less than about0.08 ps/km^(1/2) (unspun), even more preferably less than about 0.05ps/km^(1/2) (unspun), still more preferably less than about 0.03ps/km^(1/2) (unspun), even still preferably less than about 0.02ps/km^(1/2) (unspun). In preferred embodiments, these values of PMD areachieved with an effective area of greater than about 90 μm².

In one preferred embodiment, the optical waveguide fiber disclosedherein relates to a single mode optical waveguide fiber having aneffective area greater than or equal to about 90 μm² and a PMD of lessthan about 0.05 ps/km^(1/2) (unspun).

In another preferred embodiment, the optical waveguide fiber disclosedherein relates to a single mode optical waveguide fiber having aneffective area greater than or equal to about 90 μm² and which a PMD ofless than about 0.02 ps/km^(1/2) (unspun).

In preferred embodiments, the fibers disclosed herein have cabled cutoffwavelength of less than or equal to about 1500 nm, more preferablybetween about 1200 nm and about 1500 nm, even more preferably betweenabout 1250 nm and about 1400 nm, and still more preferably between about1300 nm and about 1375 nm. The zero dispersion wavelength of the fibersdisclosed herein is preferably between about 1200 and about 1350 nm. Thezero dispersion wavelength of one preferred embodiment of the opticalwaveguide fiber disclosed herein is around 1290 to 1300 nm.

Preferably, the macrobending loss of the optical waveguide fiberdisclosed herein is less than about 30 dB/m, more preferably less thanabout 20 dB/m, even more preferably less than about 15 dB/m, yet stillmore preferably less than about 10 dB/m, even more preferably less thanabout 8 dB/m, yet even more preferably less than about 5 dB/m, and mostpreferably less than about 3 dB/m.

In preferred embodiments, the radii, relative refractive indices, andrefractive profiles may be adjusted to achieve the following preferredresults: a maximum relative index Δ₁% of about 0.28; a core radius ofabout 5.5 μm; a total dispersion at 1560 nm of about 19.3 ps/nm-km; aslope at 1550 nm of about 0.060 ps/nm²-km; an effective area of about101 μm²; an attenuation of less than or equal to about 0.188 dB/km;polarization mode dispersion of less than about 0.025 ps/km^(1/2); acable cutoff wavelength of about 1366 nm; and, a mode field diameter ofabout 11.4 μm. The wavelength at zero dispersion, λ₀, of arepresentative optical waveguide fiber disclosed herein was measured bya 2-meter test to be about 1296 nm. A primary coating having a Young'smodulus of around 1.2 MPa and a secondary coating having a Young'smodulus of around 950 MPa were found to be advantageous in one or morepreferred embodiments. Macrobend values less than 7.75 dB/m using a 20mm mandrel, 5 turn test were achieved. Microbend values less than 3.0dB/m using a lateral load test were achieved.

The optical waveguide fiber disclosed herein has design parameters thatpermit about 25% larger mode field over typical known fibers, especiallythose having germania doped profiles, thereby providing significantadvantages in the Erbium amplifier window.

The waveguide optical fiber having an optical profile as described aboveis also coated with a relatively soft primary coating and a relativelyhard secondary coating which surrounds the primary coating. Commonlyassigned U.S. patent application Nos. 60/173,673, 60/173,828 and60/174,008, which are hereby incorporated by reference, describesuitable primary coatings in detail. Preferably, the modulus ofelasticity of the secondary coating of the optical waveguide fiberdisclosed herein is greater than 700 Mpa, more preferably greater than800 Mpa, and most preferably over 900 MPa. Commonly assigned U.S. patentapplication No. 60/173,874, which is hereby incorporated by reference,describes in detail suitable secondary coatings having high moduli ofelasticity.

The primary coating, sometimes referred to as the inner primary coating,is a soft cushioning layer which preferably has a Young's modulus ofless than about 5 MPa, more preferably less than about 3 MPa, and evenmore preferably less than about 1.5 MPa.

A primary coating composition for the optical waveguide fiber disclosedherein preferably comprises an oligomer and at least one monomer. Thecomposition may also contain a polymerization initiator which issuitable to cause polymerization (i.e., curing) of the composition afterits application to a glass fiber. Polymerization initiators suitable foruse in the primary coating compositions of the optical waveguide fiberdisclosed herein include thermal initiators, chemical initiators,electron beam initiators, and photoinitiators. Particularly preferredare the photoinitiators, particularly those activated by UV radiation.The coating composition may also include an adhesion promoter.

The primary coating composition may desirably contain at least oneethylenically unsaturated oligomer and at least one ethylenicallyunsaturated monomer, although more than one oligomer component and/ormore than one monomer can be introduced into the composition.

Thus, for example, an oligomer, monomer, and photoinitiator are combinedto form a bulk composition. To this bulk composition, an amount ofadhesion promoter, for example 1.0 part per hundred, is introduced inthe bulk composition.

In addition to the above-described components, the primary coatingcomposition of the optical waveguide fiber disclosed herein canoptionally include any number of additives, such as reactive diluents,antioxidants, catalysts, lubricants, co-monomers, low molecular weightnon-crosslinking resins, and stabilizers. Some additives (e.g. chaintransfer agents, for example) can operate to control the polymerizationprocess, thereby affecting the physical properties (e.g., modulus, glasstransition temperature) of the polymerization product formed from theprimary coating composition. Others can affect the integrity of thepolymerization product of the primary coating composition (e.g., protectagainst de-polymerization or oxidative degradation). Other additives mayinclude tackifier, reactive or non-reactive surfactant carriers.

The secondary coating is sometimes referred to as the outer primarycoating. The secondary coating material is typically the polymerization(i.e., cured) product of a coating composition that contains urethaneacrylate liquids whose molecules become cross-linked when polymerized.

Typical secondary coatings will include at least one UV curable monomerand at least one photoinitiator. The secondary coating may also includeabout 1-90 weight percent of at least one UV curable oligomer. It ispreferred that the secondary coating is not a thermoplastic resin.Preferably, both the monomer and the oligomer are compounds capable ofparticipating in addition polymerization. The monomer or the oligomermay be the major component of the secondary coating. An example of asuitable monomer is an ethylenically unsaturated monomer. Ethylenicallyunsaturated monomers may contain various functional groups, which enabletheir cross-linking. The ethylenically unsaturated monomers arepreferably polyfunctional (i.e., each containing two or more functionalgroups), although monofunctional monomers can also be introduced intothe composition. Therefore, the ethylenically unsaturated monomer can bea polyfunctional monomer, a monofunctional monomer, and mixturesthereof. Suitable functional groups for ethylenically unsaturatedmonomers used in accordance with the optical waveguide fiber disclosedherein include, without limitation, acrylates, methacrylates,acrylamides, N-vinyl amides, styrenes, vinyl ethers, vinyl esters, acidesters, and combinations thereof (i.e., for polyfunctional monomers).

In general, individual monomers capable of about 80% or more conversion(i.e., when cured) are more desirable than those having lower conversionrates. The degree to which monomers having lower conversion rates can beintroduced into the composition depends upon the particular requirements(i.e., strength) of the resulting cured product. Typically, higherconversion rates will yield stronger cured products.

It may also be desirable to use certain amounts of monofunctionalethylenically unsaturated monomers, which can be introduced to influencethe degree to which the cured product absorbs water, adheres to othercoating materials, or behaves under stress.

Most suitable monomers are either commercially available or readilysynthesized using reaction schemes known in the art.

Optical fiber secondary coating compositions may also contain apolymerization initiator which is suitable to cause polymerization(i.e., curing) of the composition after its application to a glass fiberor previously coated glass fiber. Polymerization initiators suitable foruse in the compositions of the optical waveguide fiber disclosed hereininclude thermal initiators, chemical initiators, electron beaminitiators, microwave initiators, actinic-radiation initiators, andphotoinitiators. Particularly preferred are the photoinitiators. Anysuitable photoinitiator can be introduced into compositions of theoptical waveguide fiber disclosed herein.

In addition to the above-described components, the secondary coatingcomposition of the optical waveguide fiber disclosed herein canoptionally include an additive or a combination of additives. Suitableadditives include, without limitation, antioxidants, catalysts,lubricants, low molecular weight non-crosslinking resins, adhesionpromoters, and stabilizers. Some additives can operate to control thepolymerization process, thereby affecting the physical properties (e.g.,modulus, glass transition temperature) of the polymerization productformed from the composition. Others can affect the integrity of thepolymerization product of the composition (e.g., protect againstde-polymerization or oxidative degradation).

The secondary coating can be a tight buffer coating or, alternatively, aloose tube coating. However, it is preferred that the outer surface ofsecondary coating not be tacky so that adjacent convolutions of theoptic fiber (i.e., on a process spool) can be unwound.

In preferred embodiments of the present invention, the primary coatingcomprises 10-90 wt % UV curable acrylate oligomer, 10-90 wt % UV curableacrylate monomer, 1-10 wt % photoinitiator, and 0-10 pph adhesionpromoter. The primary coating preferably has a Youngs Modulus of lessthan about 5 Mpa, more preferably less than about 3 MPa, and even morepreferably less than about 1.5 MPa.

In preferred embodiments of the present invention, the secondary coatingcomprises 0-90 wt % UV curable acrylate oligomer, 10-90 wt % UV curableacrylate monomer, and 1-10 wt % photoinitiator. Preferably, thesecondary coating has a Young's modulus of at least about 700 MPa, morepreferably at least about 900 MPa, and most preferably at least about1100 MPa.

Various additives that enhance one or more properties of the primary orsecondary coatings can also be present.

In preferred embodiments, the outer diameter of the overcladding ispreferably about 125 μm, the outer diameter of the primary coating ispreferably about 190 μm, and the outer diameter of the secondary coatingis preferably about 250 μm. Thus, the primary coating preferably has athickness of about 32.5 μm, and the secondary coating preferably has athickness of about 30 μm.

The outer diameter of the primary coating may preferably be within therange of about 180 μm to about 200 μm, and the outer diameter of thesecondary coating may preferably be within the range of about 245 μm toabout 255 μm.

The following examples are provided to illustrate embodiments ofcoatings of the present invention, but they are by no means intended tolimit its scope. In both the primary coating examples and the. secondarycoating examples, oligomers, monomers and photoinitators are expressedin wt % adding up to a total of 100%. Other additives are expressed inparts per hundred by weight in addition to the 100% already totaled.

Examples of Primary Coating

TABLE 4 Formulation Compositions for Primary Coatings A-D PrimaryCoating A B C D Oligomer (1)- BR3731-52% BR3731-52% BR3731-52%BR3731-52% Wt % Oligomer (2)- Wt % Monomer (1)- SR504-45% SR504-25%SR504-25% Photomer Wt % 4003-45% Monomer (2)- SR339-20% SR495-20% Wt %Photoinitiator Irgacure 1850- Irgacure 1850- Irgacure 1850- Irgacure819- (1)-Wt % 3% 3% 3% 1.5% Irgacure 184- 1.5% Adhesion a-1.0 a-1.0a-1.0 a-0.3 promoter- b-2.0 pph Antioxidant- Irganox 1035- Irganox 1035-Irganox 1035- Irganox 1035- pph 1 1 1 1

In Table 4, BR3731 is an aliphatic urethane acrylate oligomer availablefrom Bomar Specialty Co. (Winsted, Conn.); Purelast566A is an aliphaticurethane monoacrylate oligomer available from; SR504 is anethoxylatednonylphenol acrylate monomer available from; Photomer 4003 isan ethoxylated nonyl phenol acrylate monomer available from CognisCorporation (Ambler, Pa.); SR339 is a phenoxyethyl acrylate acrylatemonomer available from Sartomer Company, Inc.; CN130 is analiphaticoxyglycidyl acrylate monomer; SR495 is a caprolactone acrylatemonomer available from Sartomer Company, Inc.; Irgacure 1850 is a BAPOphotoinitiator blend containingbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide and1-hydroxycyclohexyl phenyl ketone available from Ciba SpecialtyChemicals (Tarrytown, N.Y.); Irgacure 819 is abis(2,4,6-trimethylbenzoyl)-phenyl phosphine oxide photoinitiatoravailable from Ciba Specialty Chemicals (Tarrytown, N.Y.); Irgacure 184is a 1-hydroxycyclohexyl phenyl ketone photoinitiator available fromCiba Specialty Chemicals (Tarrytown, N.Y.); “a” is a3-mercaptopropyltrimethoxysilane adhesion promoter available from UnitedChemical Technologies (Bristol, Pa.); “b” is a bis(rimethoxysilyethyl)benzene adhesion promoter available from Gelest, Inc. (Tullytown, Pa.);and Irganox 1035 is an antioxidant containing thiodiethylenebis(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate available from CibaSpecialty Chemicals.

TABLE 5 Cured Film Properties of Primary Coatings A-D Primary Coating AB C D Young's 0.82 1.21 1.29 1.23 Modulus (MPa) Y.M. stnd dev 0.03 0.070.07 0.06 Tensile Strength 0.63 1.06 0.82 0.89 (MPa) T. Strength stnd0.22 0.3 0.22 0.25 dev % Elongation 184 164 123 137 % E. stnd dev 45.5140.36 32.39 34 Tg^(a) (° C.) −34 −24 −36 −35 ^(a)T_(g)'s (glasstransition temperatures) were measured by dynamic mechanical analysis at1 Hz.

Examples of Secondary Coating

TABLE 6 Secondary Coating Composition Formulations Components Oligomerwt % Monomer(s) wt % Photoinitiator wt % Additive(s) pph A BR301 10%SR601 30% Irgacure 1850 3% — SR602 27% SR349 30% B Photomer 6010 10%Photomer 4025 20% Irgacure 1850 3% — Photomer 4028 42% RCC12-984 25% C — SR601 30% Irgacure 1850 3% — SR602 37% SR349 15% SR399 15% D BR30118.2% Photomer 4025 15.4% Irgacure 1850 2.7% — Photomer 4028 36.4%RCC12-984 27.3% F KWS 4131 10% Photomer 4028 82% Irgacure 819 1.5%Irganox 1035 0.5 Photomer 3016  5% Irgacure 184 1.5%

Of the oligomers listed in Table 6, BR301 is an aromatic urethaneacrylate oligomer available from Bomar Specialty Co., Photomer 6010 isan aliphatic urethane acrylate oligomer available from CognisCorporation, and KWS4131 is an aliphatic urethane acrylate oligomeravailable from Bomar Specialty Co.

Of the monomers listed in Table 6, SR601 is an ethoxylated(4) bisphenolA diacrylate monomer available from Sartomer Company, Inc., SR602 is aethoxylated(10) bisphenol A diacrylate monomer available from SartomerCompany, Inc., SR349 is an ethoxylated(2) bisphenol A diacrylate monomeravailable from Sartomer Company, Inc., SR399 is a dipentaerythritolpentaacrylate available from Sartomer Company, Inc., Photomer 4025 is anethoxylated(8) bisphenol A diacrylate monomer available from CognisCorporation, Photomer 4028 is an ethoxylated(4) bisphenol A diacrylatemonomer available from Cognis Corporation, RCC12-984 is anethoxylated(3) bisphenol A diacrylate monomer available from CognisCorporation, and Photomer 3016 is an epoxy acrylate available fromCognis Corporation.

Of the photoinitiators listed in Table 6, Irgacure 1850 is a blend of1-hydroxycyclohexyl phenyl ketone andbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxideavailable from Ciba Specialty Chemical, Irgacure 819 is abis(2,4,6-trimethylbenzoyl)-phenyl phosphine oxide photoinitiatoravailable from Ciba Specialty Chemicals, and Irgacure 184 is a1-hydroxycyclohexyl phenyl ketone photoinitiator available from CibaSpecialty Chemicals.

Of the additives listed in Table 6, Irganox 1035 is an antioxidantcontaining thiodiethylene bis(3,5-di-tert-butyl-4-hydroxy)hydrocinnamateavailable from Ciba Specialty Chemical.

The tested properties of the secondary coating composition formulationsare listed in Table 7.

TABLE 7 Properties of Secondary Coatings/Composition Young's WaterViscosity at Elongation Tensile Modulus Absorption 25°/45° C. (%)Strength (MPa) (MPa) (%) (poise) A 25.83 27.47 958.88 1.66 23.7/3.8 B22.41 17.01 803.52 — 20.2/3.8 C 10.34 27.56 1229.41 1.81 13.2/2.6 D 22.528.78 997.05 1.73 45.0/6.5 E 12.7 25.26 1207 — —

One preferred example of the present invention comprises a GeO₂ dopedcore and a clad layer surrounding and in contact with the core, aprimary coating having a Young's modulus of about 1.2 MPa surroundingthe clad layer, and a secondary coating having a Young's modulus ofabout 950 MPa surrounding the primary coating, wherein the core andcladding have a step index profile having a maximum relative refractiveindex of about 0.28% and a core radius of about 5.5 μm.

We have found that by combining a step index, GeO₂ doped profile withsecondary coatings having a Young's modulus of at least about 700 MPa,we can obtain increased effective area (A_(eff)), decreased bend loss,and attenuation less than about 0.185 dB/km. In particular, microbendlateral load losses of less than about 0.37 dB/m were achieved.Consequently, the Young's modulus of the secondary coating is preferablyat least about 700 MPa, more preferably at least about 900 MPa, and mostpreferably at least about 1100 MPa.

As shown in FIG. 3, and in accordance with the present invention, anoptical fiber 32 is manufactured in accordance with the presentinvention and used in an optical fiber communication system 30. System30 includes a transmitter 34 and a receiver 36, wherein optical fiber 32allows transmission of an optical signal between transmitter 34 andreceiver 36. In most systems, each end of fiber 32 will be capable of2-way communication, and transmitter 34 and receiver 36 are shown forillustration only. In at least one preferred embodiment, an opticalfiber communication system according to the present invention comprisesa transmitter and receiver connected by an optical fiber without thepresence of a regenerator therebetween. In another preferred embodiment,an optical fiber communication system according to the present inventioncomprises a transmitter and receiver connected by an optical fiberwithout the presence of an amplifier therebetween. In yet anotherpreferred embodiment, an optical fiber communication system according tothe present invention comprises a transmitter and receiver connected byan optical fiber having neither an amplifier nor a regenerator nor arepeater therebetween.

In a preferred embodiment, substantially no fluorine is present from thecenterline of the fiber disclosed herein to the outer radius of thecladding. In another preferred embodiment, substantially no fluorine ispresent from the centerline of the fiber to a radius of about 125 μm. Inyet another preferred embodiment, no fluorine is present from thecenterline of the fiber disclosed herein to the outer radius of thecladding. In still another preferred embodiment, no fluorine is presentfrom the centerline of the fiber to a radius of about 125 μm.

In another preferred embodiment, substantially no fluorine is presentfrom the centerline of the fiber disclosed herein to a radius of about50 μm. In yet another preferred embodiment, no fluorine is present fromthe centerline of the fiber to a radius of about 50 μm.

In another preferred embodiment, substantially no fluorine is presentfrom the centerline of the fiber disclosed herein to a radius of about25 μm. In yet another preferred disclosed, no fluorine is present fromthe centerline of the fiber to a radius of about 25 μm.

In another preferred embodiment, substantially no fluorine is presentfrom the centerline of the fiber disclosed herein to a radius of about10 μm. In yet another preferred embodiment, no fluorine is present fromthe centerline of the fiber to a radius of about 10 μm.

Preferably, the optical waveguide fiber disclosed herein is anon-dispersion-shifted fiber.

Preferably, the fibers disclosed herein have a low water content, andpreferably are low water peak optical fibers, i.e. having an attenuationcurve which exhibits a relatively low, or no, water peak in a particularwavelength region. Thus, the fibers disclosed herein are preferably lowwater peak fibers.

Methods of producing low water peak optical fiber can be found in U.S.application Ser. No. 09/722,804 filed Nov. 27, 2001, U.S. applicationSer. No. 09/547,598 filed Apr. 11, 2000, U.S. Provisional ApplicationSerial No. 60/258,179 filed Dec 22, 2000, and U.S. ProvisionalApplication Serial No. 60/275,015 filed Feb. 28, 2001, the contents ofeach being hereby incorporated by reference.

As exemplarily illustrated in FIG. 4, soot preform or soot body 21 ispreferably formed by chemically reacting at least some of theconstituents of a moving fluid mixture including at least oneglass-forming precursor compound in an oxidizing medium to form asilica-based reaction product. At least a portion of this reactionproduct is directed toward a substrate, to form a porous silica body, atleast a portion of which typically includes hydrogen bonded to oxygen.The soot body may be formed, for example, by depositing layers of sootonto a bait rod via an OVD process. Such an OVD process is illustratedin FIG. 4.

As shown in FIG. 4 a substrate or bait rod or mandrel 31 is insertedthrough a glass body such as hollow or tubular handle 33 and mounted ona lathe (not shown). The lathe is designed to rotate and translatemandrel 31 in close proximity with a soot-generating burner 35. Asmandrel 31 is rotated and translated, silica-based reaction product 37,known generally as soot, is directed toward mandrel 31. At least aportion of silica-based reaction product 37 is deposited on mandrel 31and on a portion of handle 33 to form a body 21 thereon. Other methodsof chemically reacting at least some of the constituents of a movingfluid mixture, such as, but not limited to, liquid delivery of at leastone glass-forming precursor compound in an oxidizing medium can be usedto form the silica-based reaction product of the present invention, asdisclosed, for example, in U.S. Provisional Patent application SerialNo. 60/095,736, filed on Aug. 7, 1997, and PCT Application Serial No.PCT/US98/25608, filed on Dec. 3, 1998, the contents of which are herebyincorporated by reference.

Once the desired quantity of soot has been deposited on mandrel 31, sootdeposition is terminated and mandrel 31 is removed from soot body 21.

As depicted in FIGS. 5 and 6 upon removal of mandrel 31, soot body 21defines a centerline hole 40 passing axially therethrough. Preferably,soot body 21 is suspended by handle 33 on a downfeed handle 42 andpositioned within a consolidation furnace 44. The end of centerline hole40 remote from handle 33 is preferably fitted with a bottom plug 46prior to positioning soot body 21 within consolidation furnace 44.Preferably, bottom plug 46 is positioned and held in place with respectto soot body 21 by friction fit. Plug 46 is further preferably taperedto facilitate entry and to allow at least temporary affixing, and atleast loosely, within the soot body 21.

Soot body 21 is preferably chemically dried, for example, by exposingsoot body 21 to a chlorine containing atmosphere at elevated temperaturewithin consolidation furnace 44. Chlorine containing atmosphere 48effectively removes water and other impurities from soot body 21, whichotherwise would have an undesirable effect on the properties of opticalwaveguide fiber manufactured from soot body 21. In an OVD formed sootbody 21, the chlorine flows sufficiently through the soot to effectivelydry the entire blank, including the centerline region surroundingcenterline hole 40.

Following the chemical drying step, the temperature of the furnace iselevated to a temperature sufficient to consolidate the soot blank intoa sintered glass preform, preferably about 1500° C. The centerline hole40 is closed during the consolidation step. In a preferred embodiment,the centerline region has a weighted average OH content of less thanabout 1 ppb.

Preferably, the centerline hole does not have an opportunity to be rewetby a hydrogen compound prior to centerline hole closure.

Preferably, exposure of the centerline hole to an atmosphere containinga hydrogen compound is significantly reduced or prevented by closing thecenterline hole during consolidation.

In a preferred embodiment, a glass body such as bottom plug 46 ispositioned in centerline hole 40 at the end of soot body 21 remote fromhandle 33, and a glass body such as hollow tubular glass plug or topplug 60 having a open end 64 is positioned in centerline hole 40 in sootbody 21 opposite plug 46 as shown in FIG. 5. Top plug 60 is showndisposed within the cavity of tubular handle 33. Following chlorinedrying, soot body 21 is down driven into the hot zone of consolidationfurnace 44 to seal centerline hole 40 and consolidate soot body 21 intoa sintered glass preform. Drying and consolidation may optionally occursimultaneously. During consolidation, soot body 21 contracts somewhatand engages bottom plug 46 and the lower end of top plug 60, therebyfusing the resulting sintered glass preform to plug 46 and plug 60 andsealing the centerline hole 40. Sealing of both the top and bottom ofcenterline hole 40 can be accomplished with one pass of soot body 21through the hot zone. Preferably, sintered glass preform is held at anelevated temperature, preferably in a holding oven, to allow inert gasto diffuse from centerline hole 40 to form a passive vacuum withinsealed centerline hole 40. Preferably, top plug 60 has a relatively thinwall through which diffusion of the inert gas can more expedientlyoccur. As depicted in FIG. 6 top plug 60 preferably has an enlargedportion 62 for supporting plug 60 within handle 33, and a narrow portion64 extending into centerline hole 40 of soot body 21. Plug 60 alsopreferably includes an elongated hollow portion 66 which may preferablyoccupy a substantial portion of handle 33. Hollow portion 66 providesadditional volume to centerline hole 40 thereby providing a bettervacuum within centerline hole 40 following diffusion of the inert gas.

The volume provided by elongated portion 66 of plug 60 provides addedvolume to sealed centerline hole 40, advantages of which will bedescribed in greater detail below.

As described above and elsewhere herein, bottom plug 46 and top plug 60are preferably glass bodies having a water content of less than about 31ppm by weight, such as fused quartz plugs, and preferably less than 5ppb by weight, such as chemically dried silica plugs. Typically, suchplugs are dried in a chlorine-containing atmosphere, but an atmospherecontaining other chemical drying agents are equally applicable. Ideally,the glass plugs will have a water content of less than 1 ppb by weight.In addition, the glass plugs are preferably thin walled plugs ranging inthickness from about 200 μm to about 2 mm. Even more preferably, atleast a portion of plug 60 has a wall thickness of about 0.2 to about0.5 mm. More preferably still, elongated portion 66 has a wall thicknessof about 0.3 mm to about 0.4 mm. Thinner walls promote diffusion, butare more susceptible to breakage during handling.

Thus, inert gas is preferably diffused from the centerline hole afterthe centerline hole has been sealed to create a passive vacuum withinthe centerline hole, and thin walled glass plugs can facilitate rapiddiffusion of the inert gas from the centerline hole. The thinner theplug, the greater the rate of diffusion.

Even after having sealed the centerline hole at both ends, thecenterline hole region of the sintered glass preform can be rewet byhydroxyl ions migrating or emanating from the glassware which is incontact with the centerline hole, the glassware being other than thesilica material which is further formed into optical waveguide fiber.Thus, for example, hydroxyl ions in the glass body such as the top plug60 could migrate to, and to contaminate or rewet, the centerline holeregion of the sintered glass preform 21. By substantially replacing theOH ions in glass bodies such as plug 60 before inserting same into,onto, or near the soot body 21, rewetting of the centerline hole regioncould be even further prevented.

Thus, optical waveguide fiber which has been subsequently drawn from apreform formed in the above manner exhibits lower optical attenuationcompared to fiber drawn from preforms which had no deuterated glassbodies in contact with and/or sealing the centerline hole. Inparticular, ultra low optical attenuation at or around 1383 nm can beachieved by preferably utilizing at least one deuterated glass body inthe manner described above. Consequently, overall lower O—H overtoneoptical attenuation can be achieved. For example, the water peak at 1383nm, as well as at other OH induced water peaks, such as at 950 nm or1240 nm, can be lowered according to the present invention, and evenvirtually eliminated.

Even more preferably, all glass bodies which are to be placed in contactwith the centerline hole before disposing same in, on, or near a sootbody or silica-based reaction product or sintered glass preform arepre-deuterized.

It should be noted that providing one or more deuterated bodies fordisposing in, on or proximate a soot body or sintered glass preform orreaction product(s) in order to obtain the beneficial results discussedabove is not limited to an OVD process, and furthermore is not limitedto a particular means of sealing the centerline hole, passively oractively inducing a vacuum in the centerline hole, or otherwise closingthe centerline hole. For example, additional methods for closing thecenterline hole are disclosed in U.S. Provisional Patent Application No.60/131,012, filed Apr. 26, 1999, titled “Optical Fiber HavingSubstantially Circular Core Symmetry and Method of Manufacturing Same”,and in U.S. patent application Ser. No. 547,598, filed on Apr. 11, 2000,entitled “Low Water Peak Optical Waveguide and Method of Making Same”,and U.S. Provisional Patent Application No. 60/131,033, filed Apr. 26,1999, the contents of which are hereby incorporated by reference.

In one preferred embodiment, plug 60 was exposed to 5% deuterium in ahelium atmosphere at 1 atm at about 1000° C. for about 24 hours. Inanother preferred embodiment, plug 60 was exposed to 3% deuterium in anitrogen atmosphere at 1 atm at about 1000° C. for about 24 hours.

At redraw, the sintered glass preforms formed as described above aresuspended within a furnace 68 by downfeed handles 42. The temperaturewithin furnace 68 is elevated to a temperature which is sufficient tostretch the glass preforms, preferably about 1950° C. to about 2100° C.,and thereby reduce the diameters of the preforms to form a cylindricalglass body such as a core cane. A sintered or consolidated glasspreform, corresponding to soot body 21, is heated and stretched to forma reduced core cane having a centerline region. Centerline hole 40closes to form the centerline region during the redraw process. Thereduced pressure maintained within sealed centerline hole 40 createdpassively during consolidation, is generally sufficient to facilitatecomplete centerline hole 40 closure during redraw.

The reduced diameter core cane, a portion of which preferablyconstitutes cladding, produced by any of the above-described embodimentscan be overclad, such as by further soot deposition, for example by anOVD process or with a rod-in-tube arrangement, and subsequently drawninto an optical waveguide fiber having a central core portion bounded bya cladding glass.

As shown FIG. 7, cylindrical optical fiber body 80 includes a silicacontaining glass region 82, at least a portion of which includeshydrogen bonded to oxygen. Silica containing glass region 82 includes acenterline region 84 having a weighted average OH content of less thanabout 2 ppb, and preferably less than about 1 ppb. Centerline region 84bounds a smaller diameter dopant (preferably germania) containing region86 (depicted by radial distance Rj), and both centerline region 84 anddopant containing region 86 extend longitudinally along central axis 28of cylindrical optical fiber body 80.

Centerline region 84, represented by radial distance R2 as depicted inFIG. 4 is defined as that portion of the optical fiber body 80 whereinabout 99% of the propagated light travels.

The optical fiber body 80 represents either a glassy preform whichserves as a precursor to an optical waveguide fiber, or the fiberitself, as the relative dimensions of the regions at a givencross-section are at least generally preserved after drawing the opticalfiber preform into a fiber.

In at least one preferred embodiment, the centerline region 84 containsno fluorine dopant. In another preferred embodiment, the dopantcontaining region 86 contains no fluorine dopant. In yet anotherpreferred embodiment, the region surrounding centerline region 84contains no fluorine dopant. In still another preferred embodiment, thecylindrical glass body 21 contains no fluorine dopant.

In at least one preferred embodiment, the cylindrical glass body 21contains no phosporus.

In another preferred embodiment, the core and cladding each have arespective refractive index which form a step-index profile.

The drawn optical waveguide fiber is then preferably deuterized.Deuteration can be carried out by a number of various processes, and maybe achieved by maintaining a silica body or part thereof at an elevatedtemperature in an atmosphere comprising deuterium. Appropriate heattreating times and temperatures can be determined from data available inthe literature. DO/OH exchange in silica may occur at temperatures aslow as 150° C., although treatment is more preferably carried out athigher temperatures, typically above about 500° C. The atmosphere can beeither substantially D2 or may also comprise inert diluents, e.g., N₂ orAr. The time required for substantially complete deuterium/hydrogen(D/H) exchange throughout a volume of silica depends substantiallyexponentially on the temperature, at least approximately on the squareof the diffusion distance, and approximately proportionally to the OH—concentration initially present in the silica body. The skilled artisancan estimate required heat treating times from data available in theliterature. The required time also depends to some degree on theconcentration of deuterium in contact with the silica body. Typically, adeuterium partial pressure of at least about 10 Torr can produceeffective infusion of deuterium at appropriate temperatures.

Thus, for a given D2 concentration, treatment times and temps could alsobe varied with equivalently effective results, independent of thecarrier gas type. D2 concentration could be also be varied withcorrespondingly varied time and temp and yield equivalently effectiveresults.

In preferred embodiments, the resulting fiber exhibits an opticalattenuation at a wavelength of about 1383 nm which is less than or equalto an optical attenuation exhibited at a wavelength of about 1310 nm.

Preferably, the optical waveguide fiber exhibits a maximum hydrogeninduced attenuation change of less than about 0.03 dB/km at a wavelengthof 1383 nm after being subjected to a 0.01 atm hydrogen partial pressurefor at least 144 hours. Even more preferably, the resulting fiberexhibits an optical attenuation at a wavelength of about 1383 nm whichis at least 0.04 dB/km less than the optical attenuation exhibited at awavelength of about 1310 nm. Even more preferably, the opticalattenuation exhibited at a wavelength of about 1383 nm is less than orequal to about 0.35 dB/km. Still more preferably, the opticalattenuation exhibited at a wavelength of about 1383 nm is less than orequal to about 0.31 dB/km.

FIG. 8 is a refractive index profile corresponding to one preferredembodiment of the fiber disclosed herein which was derived frommeasurements of a fabricated optical fiber preform or cane, wherein therefractive index profile was mapped to the fiber space. The outer radius18, r₁, of the core 12 is about 5.1 μm as measured from the fibercenterline to the vertical line depending from the half maximum relativeindex point of the descending portion of core 12. The half maximum pointis determined using the clad layer, i.e., Δ%=0, as referenced, shown bydashed line 17. The core 12 generally has a refractive index of about0.30% and a peak refractive index or maximum relative index Δ₁% of about0.33%, thus, relative to the Δ%=0 of the clad layer, the magnitude isabout 0.33%. Dashed vertical line 20 depends from the 0.165% point,which is half of the maximum magnitude of Δ₁%, at a radius of about 5.08μm.

Central segment 12 of the waveguide fiber core illustrated in FIG. 8 hasa step-shaped or step-index profile with an alpha of about 9.Preferably, the central segment of the core has an alpha greater thanabout 5, more preferably greater than about 6. In preferred embodiments,the alpha is between about 7 and about 14. A center line refractiveindex depression 16 with a radius of about 0.37 μm appears at or nearthe centerline of the fiber. The refractive index in the centerlinedepression is generally around 0.2%.

FIG. 9 shows the measured loss or attenuation for one preferredembodiment of the optical fiber having a refractive index profilecorresponding to FIG. 8. Attenuation in dB/km is plotted versuswavelength in nm. Measured and theoretically calculated fiberattenuation appears below in Table 8.

TABLE 8 Net Loss Wavelength Measured Loss Theoretical Loss aboveTheoretical (nm) (dB/km) (dB/km) (dB/km) 1310 0.33 0.32 0.01 1380 0.3290.271 0.058 1383 0.329 0.269 0.060 1385 0.329 0.267 0.062

As seem from Table 8, a relatively low water peak is exhibited by theoptical fiber at around 1383 nm.

Preferably, the attenuation of the optical fiber at 1383 nm is not morethan 0.1 dB/km higher than its attenuation at 1310 nm, more preferablythe attenuation of the optical fiber at 1383 nm is not more than 0.05dB/km higher than its attenuation at 1310 nm, and even more preferablythe attenuation of the optical fiber at 1383 nm is not more than 0.01dB/km higher than its attenuation at 1310 nm. Still more preferably, theattenuation of the optical fiber at 1383 nm is less than or equal to itsattenuation at 1310 nm.

Preferably, the attenuation of the optical fiber at 1380 nm is less thanor equal to about 0.40 dB/km, more preferably is less than or equal toabout 0.36 dB/km, and even more preferably is less than or equal toabout 0.34 dB/km.

A low water peak permits more efficient operation in the wavelengthrange from around 1290 nm to around 1650 nm with lower attenuationlosses, especially for transmission signals between about 1340 nm andabout 1470 nm. Furthermore, a low water peak also affords improved pumpefficiency of a pump light emitting device which is optically coupled tothe optical fiber, such as a Raman pump or Raman amplifier which mayoperate at one or more pump wavelengths. Preferably, a Raman amplifierpumps at one or more wavelengths which are about 100 nm lower than adesired operating wavelength or wavelength region. For example, anoptical fiber carrying an operating signal at wavelength of around 1550nm may be pumped with a Raman amplifier at a pump wavelength of around1450 nm. Thus, the lower fiber attenuation in the wavelength region fromabout 1400 nm to about 1500 nmn would tend to decrease the pumpattenuation and increase the pump efficiency, e.g. gain per mW of pumppower, especially for pump wavelengths around 1400 nm. Generally, forgreater OH impurities in a fiber, the water peak grows in width as wellas in height. Therefore, a wider choice of more efficient operation,whether for operating signal wavelengths or amplification with pumpwavelengths, is afforded by the smaller water peak.

In a preferred embodiment, the optical waveguide fiber disclosed hereincomprises a core having a refractive index profile defined by a radiusand a relative refractive index percent, wherein the core containsgermania, and a clad layer surrounding and in contact with the core andhaving a refractive index profile defined by a radius and a relativerefractive index percent, wherein the core and the clad layer provide aneffective area greater than about 90 μm², and wherein the attenuation ofthe optical fiber at 1383 nm is not more than 0.1 dB/km higher than itsattenuation at 1310 nm.

Pump wavelength for a Raman amplifier preferably depends upon thewavelength of the operating signal or transmission signal to beamplified. In preferred embodiments, transmission signals in thewavelength range between about 1530 nm to about 1560 nm, which may bereferred to as the C-band, Raman pump wavelength is preferably in therange of about 1420 nm to about 1450 nm; transmission signals in thewavelength range between about 1560 nm to about 1620 nm range, which maybe referred to as the L-band, Raman pump wavelength is preferably in therange of about 1450 nm to about 1510 nm; and transmission signals in thewavelength range of about 1460 nm to about 1530 nm range, which may bereferred to as the S-band, Raman pump wavelength is preferably in therange of about 1380 nm to 1400 nm.

The fibers disclosed herein exhibit low PMD values when fabricated withOVD processes. Methods and apparatus for achieving low polarization modedispersion (PMD) in an optical fiber or fiber section can be found inU.S. Provisional Application Serial No. 60/309,160 filed Jul. 31, 2001and in PCT/US00/10303 filed Apr. 17, 2000, and additional methods andapparatus relating to the centerline aperture region of a preform can befound in U.S. application No. Ser. 09/558,770, filed Apr. 26, 2000,entitled “An Optical Fiber and a Method for Fabricating a LowPolarization-Mode Dispersion and Low Attenuation Optical Fiber”, and inU.S. Provisional Application No. 60/131,033, filed Apr. 26, 1999,entitled “Low Water Peak Optical Waveguide and Method of ManufacturingSame”, all of which are incorporated herein by reference. Spinning ofthe fiber may also lower PMD values for the fiber disclosed herein. Inpreferred embodiments, fibers disclosed herein which have been spunexhibited PMD of less than or equal to 0.006 ps/km^(1/2). In onepreferred embodiment, the fiber exhibited PMD of 0.005 ps/km^(1/2).

In a preferred embodiment, the optical waveguide fiber disclosed hereincomprises a core having a refractive index profile defined by a radiusand a relative refractive index percent, wherein the core containsgermania, and a clad layer surrounding and in contact with the core andhaving a refractive index profile defined by a radius and a relativerefractive index percent, wherein the core and the clad layer PMD ofless than about 0.1 ps/km^(1/2).

FIG. 10 shows the refractive index profile of another preferredembodiment of an optical waveguide fiber as disclosed herein. Core 112has a maximum relative index Δ₁% of about 0.27%, thus, relative to theΔ₁%=0 of the clad layer 114, the magnitude is about 0.27%. Dashedvertical line 120 depends from the half-peak height 117, i.e. the 0.135%point, which is half of the maximum magnitude of A₁%, at a radius 18 ofabout 5.57 μm.

In one aspect, the present invention relates to an optical signaltransmission system. The optical signal transmission system preferablycomprises a transmitter, a receiver, and an optical transmission line.The optical transmission line is optically coupled to the transmitterand receiver. The optical transmission line preferably comprises atleast one optical fiber section having a core and a clad layer whichdefine a step-index profile that provides an effective area greater thanabout 90 μm², wherein the fiber exhibits an attenuation at 1383 nm whichis not more than 0.1 dB/km higher than its attenuation at 1310 nm. In apreferred embodiment, the optical fiber section has a refractive indexprofile as depicted in FIG. 1. Preferably, the core contains germania.The fiber section preferably contains substantially no fluorine. Thefiber section preferably exhibits a total dispersion within the range ofabout 16 ps/nm-km to about 22 ps/nm-km at a wavelength of about 1560 nm.The fiber section preferably exhibits a PMD of less than about 0.1ps/km^(1/2).

The system preferably further comprises at least one amplifier, such asa Raman amplifier, optically coupled to the optical fiber section.

The system may further preferably comprise a multiplexer forinterconnecting a plurality of channels capable of carrying opticalsignals onto the optical transmission line, wherein at least one of theoptical signals propagates at a wavelength between about 1300 nm and1625 nm. In a preferred embodiment, at least one of the optical signalspropagates at a wavelength between about 1330 nm and 1480 nm.

In a preferred embodiment, the system is capable of operating in acoarse wavelength division multiplex mode.

It is to be understood that the foregoing description is exemplary ofthe invention only and is intended to provide an overview for theunderstanding of the nature and character of the invention as it isdefined by the claims. The accompanying drawings are included to providea further understanding of the invention and are incorporated andconstitute part of this specification. The drawings illustrate variousfeatures and embodiments of the invention which, together with theirdescription, serve to explain the principals and operation of theinvention. It will become apparent to those skilled in the art thatvarious modifications to the preferred embodiment of the invention asdescribed herein can be made without departing from the spirit or scopeof the invention as defined by the appended claims.

What is claimed is:
 1. An optical waveguide fiber comprising: a corehaving a refractive index profile defined by a radius and a relativerefractive index percent, wherein the core contains germania, andwherein the core has an alpha less than about 14; and a clad layersurrounding and in contact with the core and having a refractive indexprofile defined by a radius and a relative refractive index percent;wherein the core and the clad layer provide an effective area greaterthan about 90 μm²at 1550 nm; and wherein the fiber containssubstantially no fluorine.
 2. The optical waveguide fiber of claim 1wherein the core and the clad layer provide an effective area at 1550 nmof between about 90 μm² and about 115 μm².
 3. The optical waveguidefiber of claim 1 wherein the core and the clad layer provide aneffective area of between about 95 μm² and about 110 μm².
 4. The opticalwaveguide fiber of claim 1 wherein the core and the cladding define asingle core segment.
 5. The optical waveguide fiber of claim 1 whereinthe relative refractive index of the core is within the range of fromabout 0.20% to about 0.35%.
 6. The optical waveguide fiber of claim 1wherein the relative refractive index of the core is within the range offrom about 0.24% to about 0.33%.
 7. The optical waveguide fiber of claim1 wherein the radius of the core is within the range of from about 4.0μm to about 7.0 μm.
 8. The optical waveguide fiber of claim 1 whereinthe radius of the core is within the range of from about 4.5 μm to about6.5 μm.
 9. The optical waveguide fiber of claim 1 wherein the core hasan alpha greater than about 5 and less than about
 14. 10. The opticalwaveguide fiber of claim 1 wherein the core has an alpha between about 7and about
 14. 11. The optical waveguide fiber of claim 1 wherein thefiber has a cabled cutoff wavelength of less than or equal to about 1500nm.
 12. The optical waveguide fiber of claim 11 wherein the fiber has acabled cutoff wavelength of between about 1200 nm and about 1500 nm, andwherein the fiber exhibits macrobending loss less than about 5 dB/m in a20 mm, 5 turn test, and wherein the fiber exhibits microbending loss ofless than about 3.0 dB/m.
 13. The optical waveguide fiber of claim 1wherein the fiber has a cabled cutoff wavelength of less than about 1400nm.
 14. The optical waveguide fiber of claim 11 wherein the fiber has acabled cutoff wavelength of between about 1300 nm and about 1375 nm, andwherein the fiber exhibits macrobending loss less than about 15 dB/m ina 20 mm, 5 turn test, and wherein the fiber exhibits microbending lossof less than about 3.0 dB/m.
 15. The optical waveguide fiber of claim 1wherein the fiber exhibits macrobending loss less than about 10 dB/m ina 20 mm, 5 turn test.
 16. The optical waveguide fiber of claim 1 whereinthe fiber further comprises a primary coating surrounding the clad layerand a secondary coating surrounding the primary coating, wherein theprimary coating has a modulus of elasticity of less than about 5 MPa.17. The optical waveguide fiber of claim 16 wherein the secondarycoating has a modulus of elasticity of greater than about 700 MPa. 18.The optical waveguide fiber of claim 1 wherein said fiber exhibitsmicrobending loss of less than about 1.0 dB/m.
 19. The optical waveguidefiber of claim 1 wherein the attenuation of the optical fiber at 1383 nmis not more than 0.1 dB/km higher than its attenuation at 1310 nm. 20.The optical waveguide fiber of claim 1 wherein the attenuation of theoptical fiber at 1383 nm is not more than 0.05 dB/km higher than itsattenuation at 1310 nm.
 21. The optical waveguide fiber of claim 1wherein the attenuation of the optical fiber at 1383 nm is not more than0.01 dB/km higher than its attenuation at 1310 nm.
 22. The opticalwaveguide fiber of claim 1 wherein the attenuation of the optical fiberat 1383 nm is less than or about equal to than its attenuation at 1310nm.
 23. The optical waveguide fiber of claim 1 wherein said fiberexhibits a PMD of less than about 0.05 ps/km^(1/2).
 24. The opticalwaveguide fiber of claim 1 wherein said fiber exhibits a PMD of lessthan about 0.01 ps/km^(1/2).
 25. The optical waveguide fiber of claim 1wherein the fiber exhibits an attenuation at a wavelength of about 1550nm of less than or equal to about 0.2 dB/km.
 26. The optical waveguidefiber of claim 1 wherein the fiber exhibits an attenuation at awavelength of about 1550 nm of less than about 0.185 dB/km.
 27. Theoptical waveguide fiber of claim 1 wherein the fiber exhibits a totaldispersion within the range of about 16 ps/nm-km to about 22 ps/nm-km ata wavelength of about 1560 nm.
 28. An optical waveguide fibercomprising: a core having a refractive index profile defined by a radiusand a relative refractive index percent with an alpha between about 5and 14, wherein the core contains germania and wherein the relativerefractive index of the core is within the range of about 0.20% to about0.35% and the radius of the core is within the range of from about 4.0μm to about 7.0 μm; and a clad layer surrounding and in contact with thecore and having a refractive index profile defined by a radius and arelative refractive index percent; wherein the fiber containssubstantially no fluorine.
 29. The optical waveguide fiber of claim 27wherein the relative refractive index of the core is within the range offrom about 0.24% to about 0.33%.
 30. The optical waveguide fiber ofclaim 27 wherein the radius of the core is within the range of fromabout 4.5 μm to about 6.5 μm.
 31. The optical waveguide fiber of claim27 wherein the core has an alpha between about 7 and about
 14. 32. Theoptical waveguide fiber of claim 28 wherein the core and the claddingdefine a single core segment.
 33. The optical waveguide fiber of claim28 wherein the fiber further comprises a primary coating surrounding theclad layer, and a secondary coating surrounding the primary coating. 34.The optical waveguide fiber of claim 33 wherein the primary coating hasa modulus of elasticity of less than about 5 MPa.
 35. The opticalwaveguide fiber of claim 33 wherein the secondary coating has a modulusof elasticity of greater than about 700 MPa.
 36. The optical waveguidefiber of claim 28 wherein the attenuation of the optical fiber at 1383nm is not more than 0.1 dB/km higher than its attenuation at 1310 nm.37. The optical waveguide fiber of claim 28 wherein the attenuation ofthe optical fiber at 1383 nm is not more than 0.05 dB/kmn higher thanits attenuation at 1310 nm.
 38. The optical waveguide fiber of claim 28wherein the attenuation of the optical fiber at 1383 nm is not more than0.01 dB/km higher than its attenuation at 1310 nm.
 39. The opticalwaveguide fiber of claim 28 wherein the attenuation of the optical fiberat 1383 nm is less than or about equal to than its attenuation at 1310nm.
 40. The optical waveguide fiber of claim 28 wherein s aid fiberexhibits a PMD of less than about 0.05 ps/km^(1/2).
 41. The opticalwaveguide fiber of claim 28 wherein said fiber exhibits a PMD of lessthan about 0.01 ps/km^(1/2).
 42. The optical waveguide fiber of claim 28wherein the fiber exhibits macrobending loss less than about 15 dB/m ina 20 mm, 5 turn test.
 43. The optical waveguide fiber of claim 28wherein said fiber exhibits microbending loss of less than about 1.0dB/m.
 44. An optical waveguide fiber comprising: a core having arefractive index profile defined by a radius and a relative refractiveindex percent, wherein the core contains germania, and wherein the corehas an alpha between about 7 and 14; and a clad layer surrounding and incontact with the core and having a refractive index profile defined by aradius and a relative refractive index percent; wherein the core and theclad layer provide an effective area greater than about 90 μm² at 1550nm; and wherein the fiber exhibits a PMD of less than about 0.05ps/km^(1/2).
 45. The optical waveguide fiber of claim 44 wherein thefiber contains substantially no fluorine.
 46. The optical waveguidefiber of claim 44 wherein the core and the clad layer provide aneffective area of between about 95 μm² and about 110 μm².
 47. Theoptical waveguide fiber of claim 44 wherein the core and the claddingdefine a single core segment.
 48. The optical waveguide fiber of claim44 wherein the fiber exhibits macrobending loss less than about 15 dB/min a 20 mm, 5 turn test.
 49. The optical waveguide fiber of claim 44wherein said fiber exhibits microbending loss of less than about 1.0dB/m.
 50. The optical waveguide fiber of claim 44 wherein theattenuation of the optical fiber at 1383 nm is not more than 0.1 dB/kmhigher than its attenuation at 1310 nm.
 51. An optical waveguide fibercomprising: a core having a refractive index profile defined by a radiusand a relative refractive index percent, wherein the core containsgermania; and a clad layer surrounding and in contact with the core andhaving a refractive index profile defined by a radius and a relativerefractive index percent; wherein the core and the clad layer provide aneffective area greater than about 90 μm² at 1550 nm; and wherein theattenuation of the optical fiber at 1383 nm is not more than 0.1 dB/kmhigher than its attenuation at 1310 nm.
 52. The optical waveguide fiberof claim 51 wherein the fiber contains substantially no fluorine. 53.The optical waveguide fiber of claim 51 wherein the core and the cladlayer provide an effective area of between about 95 μm² and about 110μm².
 54. The optical waveguide fiber of claim 51 wherein the core andthe cladding define a single core segment.
 55. The optical waveguidefiber of claim 51 wherein said fiber exhibits microbending loss of lessthan about 1.0 dB/m.
 56. The optical waveguide fiber of claim 51 whereinsaid fiber exhibits a PMD of less than about 0.05 ps/km^(1/2).
 57. Theoptical waveguide fiber of claim 51 wherein the core has an alpha lessthan about
 14. 58. An optical signal transmission system comprising: atransmitter; a receiver; an optical transmission line optically coupledto the transmitter and receiver, wherein the optical transmission linecomprises: at least one optical fiber section having a core and a cladlayer which define a single core segment that provides an effective areagreater than about 90 μm² at 1550 nm, wherein the fiber exhibits anattenuation at 1383 nm which is not more than 0.1 dB/km higher than itsattenuation at 1310 nm.
 59. The system of claim 58 wherein the corecontains germania.
 60. The system of claim 58 wherein the fiber containssubstantially no fluorine.
 61. The system of claim 58 wherein the fibersection exhibits a total dispersion within the range of about 16ps/nm-km to about 22 ps/nm-km at a wavelength of about 1560 nm.
 62. Thesystem of claim 58 wherein the fiber section exhibits a PMD of less thanabout 0.05 ps/km^(1/2).
 63. The system of claim 58 further comprising atleast one Raman amplifier optically coupled to the optical fibersection.
 64. The system of claim 58 further comprising a multiplexer forinterconnecting a plurality of channels capable of carrying opticalsignals onto the optical transmission line, wherein at least one of theoptical signals propagates at a wavelength between about 1300 nm and1625 nm.
 65. The system of claim 64 wherein at least one of the opticalsignals propagates at a wavelength between about 1330 nm and 1480 nm.66. The system of claim 58 wherein the system is capable of operating ina coarse wavelength division multiplex mode.
 67. The system of claim 58wherein the core and the clad layer provide an effective area of betweenabout 95 μm² and about 110 μm².